A variety of patient monitoring systems exist that allow the physiologic data of patients within a medical facility to be monitored remotely using wireless communications. These systems commonly include remote transmitters or transceivers that collect, and transmit over a wireless channel, the physiologic data of respective patients. This physiologic data may include, for example, real-time electrocardiograph (ECG) waveforms, SpO2 levels, and non-invasive blood pressure readings. The transmitted physiologic data is conveyed to one or more centralized monitoring stations within the medical facility. From such a monitoring station, a clinician can visually monitor the physiologic status, in real time, of many different patients. The monitoring stations may also run automated monitoring software for detecting and alerting personnel of certain types of physiologic events, such as the occurrence of a cardiac arrhythmia condition.
To enable patients to be monitored while ambulatory, some systems include battery-powered remote transceiver devices that are adapted to be worn by or attached to patients while ambulatory (“ambulatory transceivers”). Each ambulatory transceiver attaches to a patient by a pouch or other attachment device, and senses the patient's physiologic data via a set of ECG leads (and/or other types of sensor leads). In one common design, each lead wire of the ECG lead set is constructed of a shielded wire (typically coaxial) comprising an inner conductor surrounded by a mesh shield. The inner conductor electrically connects an ECG sensor to the ambulatory transceiver's sensor circuitry, and is used to carry ECG signals. The outer shield protects the ECG signals from radio frequency (RF) interference. In other designs, each lead wire is an unshielded, single-conductor wire.
In some prior art designs, selected portions of the ECG lead wires are used as the RF telemetry antenna. For example, in one design in which the lead wires have outer shields that are a fractional length of the total wire length, the shields of multiple lead wires are connected together to form the antenna. In another design, the multi-strand conductor of the RL (right leg) lead wire is used as the antenna. An important benefit of these designs is that they eliminate the need for a dedicated antenna mounted to or inside the transceiver's housing. In addition, a lead antenna can provide a somewhat larger aperture, and thus better RF link performance, than a housing mounted antenna.